// <copyright file="UnknownSelection.cs" company="Microsoft">
//      Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>
//---------------------------------------------------------------------

namespace Microsoft.Data.OData.Query.SemanticAst
{
    /// <summary>
    /// Singleton sentinal instance of <see cref="Selection"/> that indicates that $select has not been processed yet. Should never be exposed to the user.
    /// </summary>
    internal sealed class UnknownSelection : Selection
    {
        /// <summary>
        /// Singleton instance of <see cref="UnknownSelection"/>.
        /// </summary>
        public static readonly UnknownSelection Instance = new UnknownSelection();

        /// <summary>
        /// Creates the singleton instance of this class.
        /// </summary>
        private UnknownSelection()
        {
        }
    }
}